doc/README.SUSE: Remove how to build modules using kernel-source
    (jsc#PED-5021)
    
    Remove the first method how to build kernel modules from the readme. It
    describes a process consisting of the kernel-source installation,
    configuring this kernel and then performing an ad-hoc module build.
    
    This method is not ideal as no modversion data is involved in the
    process. It results in a module with no symbol CRCs which can be wrongly
    loaded on an incompatible kernel.
    
    Removing the method also simplifies the readme because only two main
    methods how to build the modules are then described, either doing an
    ad-hoc build using kernel-devel, or creating a proper Kernel Module
    Package.